Linebreak in multirow using tabularx

Question

I try to place the three first description in a multirow enviroment and include a linebreak.

But I did not succed in doing this without creating an error. Do you have an idea how I could do this?

% page setup 
\documentclass[a4paper, 11pt]{article}
\usepackage[margin=2cm]{geometry}

% language
\usepackage[utf8]{inputenc} 

% graphics
\usepackage{array,multirow,graphicx} 

% units 
\usepackage{siunitx}

% chemistry 
\usepackage{ghsystem}
\usepackage[version=4]{mhchem} 

% tables
\usepackage{ragged2e} 
\usepackage{booktabs, tabularx}
%____________________________________________________________________________________________________________
\newcolumntype{B}[1]{>{\scriptsize\RaggedRight\hspace{0pt}}p{#1}}
\newcolumntype{L}{>{\scriptsize\RaggedRight\hspace{0pt}}X}
\newlength\colwidth
%____________________________________________________________________________________________________________
% figures 
\usepackage{float}
%____________________________________________________________________________________________________________

\begin{document}

\begin{table}[ht!]
\settowidth\colwidth{\textbf{Solution}} % <-- need to use \textbf to get correct measurement
\begin{tabularx}{\textwidth}{@{} B{\colwidth} *{8}{L} @{}} 
\toprule 
\multirow{2}{*}{\textbf{Solution}}   & \multirow{2}{*}{\textbf{\shortstack{Molar mass \\ [$\si{\gram\per\mol}$]}}}   & \multirow{2}{*}{\textbf{ V stock \\ [$\si{\milli\liter}$] }}&      \multicolumn{3}{c}{\textbf{Amount of substance [$\si{\milli\mol}$]}  }     &       \multicolumn{3}{c}{\textbf{Mass [$\si{\gram}$]}  }           \\
\cmidrule(lr){4-6} \cmidrule(lr){7-9}
 & & & $\ce{KH2PO4}$ & $\ce{Na2HPO4}$ & $\ce{NaCl}$ & $\ce{KH2PO4}$ & $\ce{Na2HPO4}$ & $\ce{NaCl}$\\
\midrule
$\ce{KH2PO4}$ stock     &  \num{150}  & $\num{1.5}$  & -                 & $\num{}$ &  $\num{}$ & -         & $\num{}$ \\
$\ce{Na2HPO4}$ stock    &  \num{100}  & -             & $\num{1}$      & $\num{}$ & -            &\num{}     & $\num{}$ \\
\bottomrule
\end{tabularx}
\endtabularx
\end{table}

\end{document}

Answer 1

Here are two alternative suggestions:

\documentclass[a4paper, 11pt]{article}
\usepackage[margin=2cm]{geometry}

\usepackage{array,multirow} 
\usepackage{siunitx}

\usepackage[version=4]{mhchem} 
\usepackage{booktabs, tabularx}

\usepackage{makecell}
\renewcommand{\theadfont}{\bfseries}

\begin{document}

\begin{table}[ht!]
\setlength{\tabcolsep}{4.5pt}
\begin{tabularx}{\linewidth}{@{}XS[table-format=3] S[table-format=1.1] *{6}{c} @{}} 
\toprule 
\thead{Solution}   & {\thead{Molar mass\\{}  [\si{\gram\per\mol}]}}   & {\thead{ V stock\\{}  [\si{\milli\liter}]}} &      \multicolumn{3}{c}{\thead{Amount of substance\\{} [\si{\milli\mol}]}  }     &       \multicolumn{3}{c}{\thead{Mass\\{} [\si{\gram}]}  }           \\
\cmidrule(r){4-6} \cmidrule(l){7-9}
                     &       &      & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl} & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl}\\
\midrule
\ce{KH2PO4} stock    &  150  & 1.5  & -           &              &           & -           &              &     \\
\ce{Na2HPO4} stock   &  10   & {-}  & 1           &              & -         &             &              &     \\
\bottomrule         
\end{tabularx}
\end{table}


\begin{table}[ht!]
\small
\begin{tabular}{@{}l S[table-format=3] S[table-format=1.1] *{6}{c} @{}} 
\toprule 
\multirow{2.5}{*}{\thead{Solution}}   & {\multirow{2.5}{*}{\thead{Molar mass\\{}  [\si{\gram\per\mol}]}}}   & {\multirow{2.5}{*}{\thead{ V stock\\{}  [\si{\milli\liter}]}}} &      \multicolumn{3}{c}{\thead{Amount of substance [\si{\milli\mol}]}  }     &       \multicolumn{3}{c}{\thead{Mass [\si{\gram}]}  }           \\
\cmidrule(r){4-6} \cmidrule(l){7-9}
                     &       &      & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl} & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl}\\
\midrule
\ce{KH2PO4} stock    &  150  & 1.5  & -           &              &           & -           &              &     \\
\ce{Na2HPO4} stock   &  10   & {-}  & 1           &              & -         &             &              &     \\
\bottomrule         
\end{tabular}
\end{table}


\end{document}

Answer 2

Here is a solution. I have used \multirowcell from the \makecell package for the multiline \multirows and left the units outside of \textbf because units won't be done bold. The second column is fit to the "Molar mass" width.

EDIT: In fact \multirow{2}={\textbf{Molar mass} \\{}[$\si{\gram\per\mol}$] } works as well as \multirowcell, and for the other one similar.

\documentclass[a4paper, 11pt]{article}
\usepackage[margin=2cm]{geometry}

% language
\usepackage[utf8]{inputenc} 

% graphics
\usepackage{array,multirow,graphicx} 

% units 
\usepackage{siunitx}

% chemistry 
\usepackage{ghsystem}
\usepackage[version=4]{mhchem} 

% tables
\usepackage{ragged2e} 
\usepackage{booktabs, tabularx}
%____________________________________________________________________________________________________________
\newcolumntype{B}[1]{>{\scriptsize\RaggedRight\hspace{0pt}}p{#1}}
\newcolumntype{L}{>{\scriptsize\RaggedRight\hspace{0pt}}X}
\newlength\colwidth
\newlength\colwidthb
%____________________________________________________________________________________________________________
% figures 
\usepackage{float}
%____________________________________________________________________________________________________________
\usepackage{makecell}

\begin{document}

\begin{table}[ht!]
\settowidth\colwidth{\textbf{Solution}} % <-- need to use \textbf to get correct measurement
\settowidth\colwidthb{\textbf{Molar mass}} % <-- need to use \textbf to get correct measurement
\begin{tabularx}{\textwidth}{@{} B{\colwidth} @{} B{\colwidthb}@{} *{7}{L} @{}} 
\toprule 
 \multirow{2}*{\textbf{Solution}}   &
 \multirowcell{2}[0pt][l]{\textbf{Molar mass} \\{}[$\si{\gram\per\mol}$] }  &
 \multirowcell{2}[0pt][l]{\textbf{V mass} \\{}[\si{\milli\liter}] }  &
    \multicolumn{3}{c}{\textbf{Amount of substance [$\si{\milli\mol}$]}  }     &   
    \multicolumn{3}{c}{\textbf{Mass [$\si{\gram}$]}  }    
       \\
\cmidrule(lr){4-6} \cmidrule(lr){7-9}
 & & & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl} & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl} \\
\midrule
$\ce{KH2PO4}$ stock     &  \num{150}  & $\num{1.5}$  & -                 & $\num{}$ &  $\num{}$ & -         & $\num{}$ \\
$\ce{Na2HPO4}$ stock    &  \num{100}  & -             & $\num{1}$      & $\num{}$ & -            &\num{}     & $\num{}$ \\
\bottomrule
\end{tabularx}
%\endtabularx
\end{table}

\end{document}

Answer 3

With {NiceTabular} of nicematrix.

\documentclass[a4paper, 11pt]{article}
\usepackage[margin=2cm]{geometry}
\usepackage{siunitx}
\usepackage[version=4]{mhchem} 
\usepackage{booktabs}
\usepackage{nicematrix}

\begin{document}

\begin{table}[ht!]
\small
\begin{NiceTabular}{@{}l S[table-format=3] S[table-format=1.1] *{6}{c} @{}} 
\toprule 
\Block{2-1}{\bfseries Solution} 
& \Block{2-1}<\bfseries>{Molar mass\\{} [\si{\gram\per\mol}]} 
& \Block{2-1}<\bfseries>{V stock\\{} [\si{\milli\liter}]} 
& \Block{1-3}<\bfseries>{Amount of substance\\ [\si{\milli\mol}]} &&
& \Block{1-3}{\bfseries Mass\\ [\si{\gram}]} \\
\cmidrule(r){4-6} \cmidrule(l){7-9}
                     &       &      & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl} & \ce{KH2PO4} & \ce{Na2HPO4} & \ce{NaCl}\\
\midrule
\ce{KH2PO4} stock    &  150  & 1.5  & -           &              &           & -           &              &     \\
\ce{Na2HPO4} stock   &  10   & {-}  & 1           &              & -         &             &              &     \\
\bottomrule         
\end{NiceTabular}
\end{table}

\end{document}